March 04, 2013

Y chromosomes of pastoralists and farmers from the Sahel

Am J Phys Anthropol DOI: 10.1002/ajpa.22236

Multiple and differentiated contributions to the male gene pool of pastoral and farmer populations of the African Sahel

Jana Bučková et al.

The African Sahel is conducive to studies of divergence/admixture genetic events as a result of its population history being so closely related with past climatic changes. Today, it is a place of the co-existence of two differing food-producing subsistence systems, i.e., that of sedentary farmers and nomadic pastoralists, whose populations have likely been formed from several dispersed indigenous hunter-gatherer groups. Using new methodology, we show here that the male gene pool of the extant populations of the African Sahel harbors signatures of multiple and differentiated contributions from different genetic sources. We also show that even if the Fulani pastoralists and their neighboring farmers share high frequencies of four Y chromosome subhaplogroups of E, they have drawn on molecularly differentiated subgroups at different times. These findings, based on combinations of SNP and STR polymorphisms, add to our previous knowledge and highlight the role of differences in the demographic history and displacements of the Sahelian populations as a major factor in the segregation of the Y chromosome lineages in Africa. Interestingly, within the Fulani pastoralist population as a whole, a differentiation of the groups from Niger is characterized by their high presence of R1b-M343 and E1b1b1-M35. Moreover, the R1b-M343 is represented in our dataset exclusively in the Fulani group and our analyses infer a north-to-south African migration route during a recent past.

6 comments:

It isn't totally clear if this sample is from Niger only or from the entire Sahel. The data seem like a better fit for a Niger only sample.

E1b1b1a looks like the defining y-dna hg of the population that brought farming to the Sahel. It is present at about 6%-7% in the farmers and absent in the pastoralists. Then again, while it is not found in these Sahel pastoralist Fulani, it is found in about <a href="http://en.wikipedia.org/wiki/Haplogroup_E-V68_(Y-DNA)>34% of East African Fulani</a> and many other populations. Probably, in t he Fulani of Niger, this is mostly E-V22 and/or E-V32 which are subbranches of two separate subbranches of E-M35 (as distinct from mostly North African and mostly European branches of E-M35). E-V32 is found in the Nile basin, Blue Nile basin and White Nile Basin, plus Lake Chad and over into Ethiopia and the Horn of Africa; V-22 has a broadly similar distribution including 31% of Fulanis in Sudan. This suggests a demic source of Sahelian farming technology mostly from Fertile Crescent via indigenous Egyptian who adopted farming, and/or from some independent innovations in Ethiopia, as opposed to from West Africa (West African associated types of E seem similar between farmers and pastoralists).

The R1b-V88 (which is what we are seeing) look like possibly introgressions from linguistically Chadic populations, who are also Sahel pastoralists. R1b-V88 is modal in the Chadic populations of Northern Cameroon (28.6% to 95.5% in each group for which data is available) and is 20% in Northern Nigerian Chadic populations. Almost all other instances of R1b have been found in Northern Cameroon, Chad, Niger, Northern Nigeria and Southern Egypt (all of which are in or near the Lake Chad endoheric basin) and overwhelmingly among pastoralists.

Wikipeidia's R1b-V88 entry compiles just 3 instances out of 529 people sampled in North Africa outside Southern Egypt and the Siwa Oasis Berbers, none in in West Africa (sample n=123), none in East Africa (sample n=442), none in Southern Africa (sample n=105), and 2 out of 144 in a sub-Sahel region of Southern Cameroon, Southern Niger and CAR.

These Chadic populations are adjacent to some Fulani populations (in a manner similar to Siwa Berbers of Southern Egypt with 28% R1b and 4.5% in Niger Berbers but virtually absent in other Berber populations), some linguistically Semitic populations of Southern Egypt, all of which a relatively close to a Lake Chad epicenter for R1b-V88. The Hasua and Fulani have been undergoing some degree ethnic fusion in the last couple of generations due to similar Islamic religions and Sahel pastoralist lifestyles that have broken down endogamy barriers.

Andrew saidE1b1b1a looks like the defining y-dna hg of the population that brought farming to the Sahel. It is present at about 6%-7% in the farmers and absent in the pastoralists. Then again, while it is not found in these Sahel pastoralist Fulani, it is found in about 34% E-V68 of East African Fulani and many other populations. Probably, in the Fulani of Niger, this is mostly E-V22 and/or E-V32 which are subbranches of two separate subbranches of E-M35 (as distinct from mostly North African and mostly European branches of E-M35). E-V32 is found in the Nile basin, Blue Nile basin and White Nile Basin, plus Lake Chad and over into Ethiopia and the Horn of Africa; V-22 has a broadly similar distribution including 31% of Fulanis in Sudan. This suggests a demic source of Sahelian farming technology mostly from Fertile Crescent via indigenous Egyptian who adopted farming, and/or from some independent innovations in Ethiopia, as opposed to from West Africa (West African associated types of E seem similar between farmers and pastoralists).

The study says no R1b was found in Lake Chad, which is very strange because previous studies found almost 50% R1b there, but the haplotype data shows they made an incredible amount of mistakes. R1b in Lake Chad, according to their own haplotype data, I think was truly around 35% to 40%.

But the thing that caught my attention the most was the obvious presence of E-V257, the node immediately ancestral to E-M81, the most common haplogroup in North Africa. The image below explains everything.

i agree with the comments respecting the study as scientific action. I fully agree with the surprise of commenter about missing Hausa in the table despite they count millions more than Kanuri and Fulani together, and there are other studies show high frequency of R1b and subgroups of E haplogroup mentioned here among others not here like A, B subs.

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